Video-sharing services provide a platform for video content creators to distribute digitized videos to other parties over a network, such as the Internet. The video-sharing service may be implemented by a computing system comprising one or more servers in one or more locations. Content creators can upload their videos to the computing system, along with metadata that describes their videos, which the computing system uses to index the videos and make them discoverable to users who express an interest in viewing such videos. The video-sharing service can then receive search queries from users requesting video content. In some instances, the video-sharing service selects videos to serve to users based on a comparison of topics associated with the videos to topics indicated in search queries that the users have submitted to the video-sharing service.